Mad rush is only one option. Steady pace forward, checking for supplies where opportune, setting up defense positions on choke points when a horde is incoming is another.

Easy is not hard in terms of killing the infected, but you still have to stick with your mates. When a hunter jumps you from behind and you are nowhere near them, you are down and will die. Everyone doing their own thing will easily get all of you incapacitated by the special infected.

would be a hell of alot easier if there was a pointer on map at all times telling you were the objective is not just show up when you are close to it. and not all people want to play a game with random people they like to play with thier friends and take time to find extra achievments within the levels.